ASTM G93/G93M-19

Standard Guide for Cleanliness Levels and Cleaning Methods for Materials and Equipment Used in Oxygen-Enriched Environments

SIGNIFICANCE AND USE
5.1 The purpose of this guide is to furnish qualified technical personnel with pertinent information for the selection of cleaning methods for cleaning materials and equipment to be used in oxygen-enriched environments. This guide furnishes qualified technical personnel with guidance in the specification of oxygen system cleanliness needs. It does not actually specify cleanliness levels.  
5.2 Insufficient cleanliness of components used in oxygen systems can result in the ignition of contaminants or components by a variety of mechanisms such as particle, mechanical, or pneumatic impact. These mechanisms are explained in detail in Guide G88.  
5.3 Adequate contamination control in oxygen systems is imperative to minimize hazards and component failures that can result from contamination. Contamination must also be minimized to ensure an acceptable product purity.  
5.4 Removal of contaminants from materials and components depends on system configuration, materials of construction, and type and quantity of contaminant.  
5.5 Examples of cleaning procedures contained herein may be followed or specified for those materials, components, and equipment indicated. The general cleaning text can be used to establish cleaning procedures for materials, components, equipment, and applications not addressed in detail. See Guide G127 for discussion of cleaning agent and procedure selection.
SCOPE
1.1 This guide covers the selection of methods and apparatus for cleaning materials and equipment intended for service in oxygen-enriched environments. Contamination problems encountered in the use of enriched air, mixtures of oxygen with other gases, or any other oxidizing gas may be solved by the same cleaning procedures applicable to most metallic and nonmetallic materials and equipment. Cleaning examples for some specific materials, components, and equipment, and the cleaning methods for particular applications, are given in the appendixes.  
1.2 This guide includes levels of cleanliness used for various applications and the methods used to obtain and verify these levels.  
1.3 This guide applies to chemical-, solvent-, and aqueous-based processes.  
1.4 This guide describes nonmandatory material for choosing the required levels of cleanliness for systems exposed to oxygen or oxygen-enriched atmospheres.  
1.5 This guide proposes a practical range of cleanliness levels that will satisfy most system needs, but it does not deal in quantitative detail with the many conditions that might demand greater cleanliness or that might allow greater contamination levels to exist. Furthermore, it does not propose specific ways to measure or monitor these levels from among the available methods.  
1.6 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.  
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Federal, state, and local safety and disposal regulations concerning the particular hazardous materials, reagents, operations, and equipment being used should be reviewed by the user. The user is encouraged to obtain the Material Safety Data Sheet (MSDS) from the manufacturer for any material incorporated into a cleaning process. Specific cautions are given in Section 8.  
1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guide...

General Information

• Status: Published
• Publication Date: 30-Sep-2019
• ICS: 71.040.20 - Laboratory ware and related apparatus
• Technical Committee: G04 - Compatibility and Sensitivity of Materials in Oxygen Enriched Atmospheres
• Drafting Committee: G04.02 - Recommended Practices

Relations

• Replaces: ASTM G93-03(2011) - Standard Practice for Cleaning Methods and Cleanliness Levels for Material and Equipment Used in Oxygen-Enriched Environments
• Effective Date: 01-Oct-2019
• Refers: ASTM F331-13(2020) - Standard Test Method for Nonvolatile Residue of Solvent Extract from Aerospace Components (Using Flash Evaporator)
• Effective Date: 01-Apr-2020
• Refers: ASTM G136-03(2016) - Standard Practice for Determination of Soluble Residual Contaminants in Materials by Ultrasonic Extraction
• Effective Date: 01-May-2016
• Refers: ASTM G131-96(2016) - Standard Practice for Cleaning of Materials and Components by Ultrasonic Techniques
• Effective Date: 01-May-2016
• Refers: ASTM F331-13 - Standard Test Method for Nonvolatile Residue of Solvent Extract from Aerospace Components (Using Flash Evaporator)
• Effective Date: 01-Jun-2013
• Refers: ASTM D2200-13 - Standard Practice for Use of Pictorial Surface Preparation Standards and Guides for Painting Steel Surfaces
• Effective Date: 01-Jun-2013
• Refers: ASTM E312-06(2011) - Standard Practice for Description and Selection of Conditions for Photographing Specimens Using Analog (Film) Cameras and Digital Still Cameras (DSC) (Withdrawn 2017)
• Effective Date: 01-Jun-2011
• Refers: ASTM G136-03(2009) - Standard Practice for Determination of Soluble Residual Contaminants in Materials by Ultrasonic Extraction
• Effective Date: 01-Apr-2009
• Refers: ASTM F312-08 - Standard Test Methods for Microscopical Sizing and Counting Particles from Aerospace Fluids on Membrane Filters
• Effective Date: 01-Nov-2008
• Refers: ASTM G122-96(2008) - Standard Test Method for Evaluating the Effectiveness of Cleaning Agents
• Effective Date: 01-Sep-2008
• Refers: ASTM G131-96(2008) - Standard Practice for Cleaning of Materials and Components by Ultrasonic Techniques
• Effective Date: 01-Sep-2008
• Refers: ASTM D2200-08 - Standard Practice for Use of Pictorial Surface Preparation Standards and Guides for Painting Steel Surfaces
• Effective Date: 01-Jun-2008
• Refers: ASTM G127-95(2008) - Standard Guide for the Selection of Cleaning Agents for Oxygen Systems
• Effective Date: 01-Apr-2008
• Refers: ASTM G63-99(2007) - Standard Guide for Evaluating Nonmetallic Materials for Oxygen Service
• Effective Date: 15-Mar-2007
• Refers: ASTM G144-01(2006) - Standard Test Method for Determination of Residual Contamination of Materials and Components by Total Carbon Analysis Using a High Temperature Combustion Analyzer
• Effective Date: 01-Oct-2006

Overview

ASTM G93/G93M-19, published by ASTM International, is a key standard that provides guidelines for selecting cleaning methods and cleanliness levels for materials and equipment used in oxygen-enriched environments. Oxygen-enriched systems, such as those used in medical, industrial, and aerospace applications, are highly sensitive to contamination, which can cause ignition hazards or affect product purity. This standard assists qualified technical personnel in specifying and implementing appropriate cleaning procedures to minimize risks and maintain safety and reliability.

While ASTM G93/G93M-19 does not specify mandatory cleanliness levels or detailed measurement methods, it outlines practical approaches and considerations for choosing and verifying cleaning processes. The guidance applies to both metallic and nonmetallic materials, and addresses cleaning with chemical, solvent, and aqueous methods.

Key Topics

• Significance of Cleanliness: Clean materials and components are essential in oxygen-enriched systems to prevent ignition, contamination, and component failure.
• Contaminant Types: The guide categorizes contaminants as organics, inorganics, and particulates, providing practical information on their removal.
• Cleaning Methods: Discusses various mechanical and chemical cleaning techniques, including:
  • Abrasive blasting
  • Ultrasonic cleaning
  • Caustic and detergent cleaning
  • Solvent cleaning
  • Acid cleaning
  • Swab, spray, and dip cleaning
• Considerations for Method Selection: Emphasizes evaluating part material, contaminant type, required cleanliness, environmental impact, and compatibility with cleaning agents.
• Disassembly and Handling: Recommends cleaning components in a disassembled state and outlines best practices for handling, packaging, and assembly to prevent recontamination.
• Verification and Rinsing: Highlights the importance of thorough rinsing and proper drying after cleaning to avoid residue and prevent safety risks.
• Safety Precautions: Stresses the need for proper safety, health, and environmental practices, including adherence to local regulations, use of protective equipment, and review of Material Safety Data Sheets (MSDS) for cleaning agents.

Applications

ASTM G93/G93M-19 is widely used in industries where oxygen-enriched atmospheres are present. Common applications include:

• Medical Devices and Hospital Systems: Ensuring components for oxygen delivery systems are free from hazardous contaminants.
• Aerospace and Aviation: Maintaining high purity and safety in components exposed to oxygen, such as valves, piping, tanks, and life-support systems.
• Industrial Gas Production and Handling: Cleaning equipment used in oxygen manufacturing, storage, and distribution to avoid dangerous ignition and maintain product quality.
• Chemical Processing Plants: Selecting proper cleaning procedures for systems exposed to oxidizing gases, reducing the risk of fires or explosions.

Related Standards

For a comprehensive approach to cleaning and maintaining oxygen-enriched systems, the following standards provide valuable supplemental information:

• ASTM G88: Guide for Designing Systems for Oxygen Service
• ASTM G127: Guide for Selection of Cleaning Agents for Oxygen-Enriched Systems
• ASTM G63: Guide for Evaluating Nonmetallic Materials for Oxygen Service
• ASTM G121: Practice for Preparation of Contaminated Test Coupons for the Evaluation of Cleaning Agents
• ASTM G122: Test Method for Evaluating the Effectiveness of Cleaning Agents
• ASTM G131: Practice for Cleaning of Materials and Components by Ultrasonic Techniques
• CGA G-4.1 and G-4.4: Compressed Gas Association resources on cleaning equipment for oxygen service
• ISO 14644-1: Cleanrooms and Associated Controlled Environments

Practical Value

Implementing ASTM G93/G93M-19 helps organizations reduce hazards, extend component life, and maintain compliance in oxygen-enriched environments. Adopting the recommended cleaning methods and cleanliness levels ensures operational integrity, product safety, and regulatory adherence, making this standard essential for industries handling oxygen or oxidizing gases.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G93/G93M −19
Standard Guide for
Cleanliness Levels and Cleaning Methods for Materials and
Equipment Used in Oxygen-Enriched Environments
This standard is issued under the fixed designation G93/G93M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.1 This guide covers the selection of methods and appara-
mine the applicability of regulatory limitations prior to use.
tus for cleaning materials and equipment intended for service
Federal, state, and local safety and disposal regulations con-
in oxygen-enriched environments. Contamination problems
cerning the particular hazardous materials, reagents,
encounteredintheuseofenrichedair,mixturesofoxygenwith
operations, and equipment being used should be reviewed by
other gases, or any other oxidizing gas may be solved by the
the user. The user is encouraged to obtain the Material Safety
same cleaning procedures applicable to most metallic and
Data Sheet (MSDS) from the manufacturer for any material
nonmetallic materials and equipment. Cleaning examples for
incorporated into a cleaning process. Specific cautions are
some specific materials, components, and equipment, and the
given in Section 8.
cleaning methods for particular applications, are given in the
1.8 This international standard was developed in accor-
appendixes.
dance with internationally recognized principles on standard-
1.2 This guide includes levels of cleanliness used for
ization established in the Decision on Principles for the
various applications and the methods used to obtain and verify
Development of International Standards, Guides and Recom-
these levels.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.3 This guide applies to chemical-, solvent-, and aqueous-
based processes.
2. Referenced Documents
1.4 This guide describes nonmandatory material for choos-
2.1 ASTM Standards:
ing the required levels of cleanliness for systems exposed to
D1193 Specification for Reagent Water
oxygen or oxygen-enriched atmospheres.
D2200 Practice for Use of Pictorial Surface Preparation
1.5 This guide proposes a practical range of cleanliness
Standards and Guides for Painting Steel Surfaces
levels that will satisfy most system needs, but it does not deal
E312 Practice for Description and Selection of Conditions
in quantitative detail with the many conditions that might
for Photographing Specimens Using Analog (Film) Cam-
demand greater cleanliness or that might allow greater con-
eras and Digital Still Cameras (DSC) (Withdrawn 2017)
tamination levels to exist. Furthermore, it does not propose
F312 Test Methods for Microscopical Sizing and Counting
specific ways to measure or monitor these levels from among
Particles from Aerospace Fluids on Membrane Filters
the available methods.
F331 Test Method for Nonvolatile Residue of Solvent Ex-
1.6 Units—The values stated in either SI units or inch-
tract from Aerospace Components (Using Flash Evapora-
pound units are to be regarded separately as standard. The
tor)
values stated in each system are not necessarily exact equiva-
G63 Guide for Evaluating Nonmetallic Materials for Oxy-
lents; therefore, to ensure conformance with the standard, each
gen Service
system shall be used independently of the other, and values
G88 Guide for Designing Systems for Oxygen Service
from the two systems shall not be combined.
G122 Test Method for Evaluating the Effectiveness of
Cleaning Agents
1.7 This standard does not purport to address all of the
G127 Guide for the Selection of Cleaning Agents for
safety concerns, if any, associated with its use. It is the
1 2
This guide is under the jurisdiction ofASTM Committee G04 on Compatibility For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and Sensitivity of Materials in Oxygen Enriched Atmospheres and is the direct contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
responsibility of Subcommittee G04.02 on Recommended Practices. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Oct. 1, 2019. Published October 2019. Originally the ASTM website.
approved in 1987. Last previous edition approved in 2011 as G93 – 03(2011). DOI: The last approved version of this historical standard is referenced on
10.1520/G0093_G0093M-19. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G93/G93M − 19
Oxygen-Enriched Systems 3.1.6 qualified technical personnel, n—persons such as
G131 Practice for Cleaning of Materials and Components by engineers and chemists who, by virtue of education, training,
Ultrasonic Techniques or experience, know how to apply physical and chemical
G136 Practice for Determination of Soluble Residual Con- principles involved in the reactions between oxidants and other
taminants in Materials by Ultrasonic Extraction metals.
G144 Test Method for Determination of Residual Contami-
3.2 Definitions of Terms Specific to This Standard:
nation of Materials and Components by Total Carbon
3.2.1 cleanliness, n—the degree to which an oxygen system
Analysis Using a HighTemperature CombustionAnalyzer
is free of contaminant.
2.2 CGA Documents:
3.2.2 fibers, n—particulate matter with a length of 100 µm
CGA Pamphlet G-4.1 Cleaning Equipment for Oxygen Ser-
or greater, and a length-to-width ratio of 10 to 1 or greater.
vice
3.2.3 particulate, n—ageneraltermusedtodescribeafinely
CGA Pamphlet G-4.4 Industrial Practices for Gaseous Oxy-
divided solid of organic or inorganic matter.
gen Transmission and Distribution Piping Systems
3.2.3.1 Discussion—These solids are usually reported as the
2.3 SAE Document:
amount of contaminant by the population of a specific microm-
ARP598 TheDeterminationofParticulateContaminationin
eter size. See methods described inTest Methods F312 orARP
Liquids by the Particle Count Method
6 598 for particle size and population determination.
2.4 ISO Document:
ISO 14644-1 Cleanrooms and Associated Controlled
4. Summary of Guide
Environments—Part 1: Classification of Air Cleanliness
4.1 General methods, apparatus, and reagents for cleaning
3. Terminology
materials and equipment used in oxygen-enriched environ-
ments are described in this guide. Exact procedures are not
3.1 Definitions:
given because they depend on the contaminant type and
3.1.1 contaminant, n—unwanted molecular or particulate
material to be cleaned, cleaning agent used, and degree of
matterthatcouldadverselyaffectordegradetheoperation,life,
cleanliness required. Methods may be used individually, or
or reliability of the systems or components upon which it
may be combined or repeated to achieve the desired results.
resides.
Examples of cleaning procedures that have been successfully
3.1.2 contamination, n—(1) the amount of unwanted mo-
used for specific materials, components, and equipment in
lecular or particulate matter in a system; (2) the process or
selected applications are described in the appendices.An index
condition of being contaminated.
of the specific materials, components, equipment, and applica-
3.1.2.1 Discussion—Contamination and cleanliness are op-
tions covered in these examples is given in Table X1.1.
posing properties; increasing cleanliness implies decreasing
contamination. 4.2 For the purpose of this guide, both solid and fluid
contaminants have been subclassed into three categories:
3.1.3 direct oxygen service, n—service in contact with
organics, inorganics, and particulates. A list of common con-
oxygen-enriched atmosphere during normal operation.
tamination levels is given in Table 1.
3.1.3.1 Discussion—Examples are oxygen compressor pis-
ton rings or control valve seats.
4.3 Cleanliness specifications that have been used in the
past are identified, levels of cleanliness that can be achieved
3.1.4 nonmetal, n—any material other than a metal, non-
are listed along with factors that suggest potential upper limits
polymeric alloy, or any composite in which the metallic
for allowable system contamination, and the practical difficul-
component is not the most easily ignited component and for
ties in adopting and achieving adequately clean systems are
which the individual constituents cannot be evaluated
reviewed. Cleanliness specifications used by suppliers and
independently, including ceramics (such as glass), synthetic
manufacturers often differ; it is therefore important to commu-
polymers (such as most rubbers, thermoplastics, and
nicate and agree upon which specification is to be used for a
thermosets), and natural polymers (such as naturally occurring
given system and to adhere to the most conservative measures.
rubber, wood, and cloth).
3.1.4.1 Discussion—Nonmetallic is the adjective use of this
term.
A
TABLE 1 Oil Film Contamination Level Specifications
3.1.5 oxygen compatibility (also oxidant compatibility),
Concentration,
n—the ability of a substance to coexist with both oxygen and
Source
2 2
mg/m (mg/ft )
a potential source(s) of ignition at an expected pressure and
0.14 (0.013) 1967 Navy Standard per Presti and DeSimone (1)
temperature with a magnitude of risk acceptable to the user.
10.8 (1) NASA KSC 123 per Report MTB 306-71 (2)
16.1 (1.5) Recommended by Presti and DeSimone (1)
43.1 (4) Air Force 1950s value per LeSuer (3)
75.3 (7) Recommended by Walde (4)
Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5th
108 (10 mg/ft or per item) Union Carbide Guideline (5,6)
Floor, Chantilly, VA 20151-2923, http://www.cganet.com.
50 to 100 (4.6 to 9.3) Compressed Gas Association Pamphlet G-4.8 (7)
Available from SAE International (SAE), 400 Commonwealth Dr.,Warrendale,
500 (47.5) Compressed Gas Association Pamphlet G-4.1 (8)
PA 15096-0001, http://www.sae.org.
A
Available from International Organization for Standardization (ISO), 1, ch. de
The boldface numbers in parentheses refer to the list of references at the end of
la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://
this standard.
www.iso.ch.
G93/G93M − 19
5. Significance and Use ticles. Such methods can damage sealing surfaces, remove
protective coatings, and work-harden metals. Sensitive sur-
5.1 The purpose of this guide is to furnish qualified techni-
faces must be protected before mechanical cleaning methods
cal personnel with pertinent information for the selection of
are applied.
cleaning methods for cleaning materials and equipment to be
6.2.2 Chemical cleaners, both acid and caustic, can damage
used in oxygen-enriched environments. This guide furnishes
metal parts if not neutralized upon completion of cleaning.
qualified technical personnel with guidance in the specification
Corrosion, embrittlement, or other surface modifications are
of oxygen system cleanliness needs. It does not actually
potentially harmful side effects of chemical cleaning agents.
specify cleanliness levels.
Crevice corrosion can occur and sealing surfaces can be etched
5.2 Insufficient cleanliness of components used in oxygen
enough to destroy the finish necessary to seal the part. SeeTest
systems can result in the ignition of contaminants or compo-
Method G122 and Guide G127 for methods used to evaluate
nents by a variety of mechanisms such as particle, mechanical,
cleaners for use on various materials used in oxygen service.
orpneumaticimpact.Thesemechanismsareexplainedindetail
6.2.3 Solvent cleaning solutions often damage plastics and
in Guide G88.
elastomers. The manufacturer should be consulted or sample
parts should be tested to ensure that the solvent is not harmful
5.3 Adequate contamination control in oxygen systems is
to the item being cleaned.
imperative to minimize hazards and component failures that
can result from contamination. Contamination must also be
6.3 Lubricants:
minimized to ensure an acceptable product purity.
6.3.1 Mechanical components are normally assembled with
lubricants on seals, threads, and moving surfaces. The manu-
5.4 Removal of contaminants from materials and compo-
facturer should be consulted to determine the kind of lubricant
nents depends on system configuration, materials of
originally used on the article to ensure that the cleaning
construction, and type and quantity of contaminant.
solutions and methods selected are effective in removing the
5.5 Examples of cleaning procedures contained herein may
lubricant and will not damage the component.
be followed or specified for those materials, components, and
6.3.2 Oxygen-compatible lubricants should be selected in
equipment indicated. The general cleaning text can be used to
accordance with Guide G63. The component manufacturer
establish cleaning procedures for materials, components,
should also be consulted to ensure that the selected lubricant
equipment, and applications not addressed in detail. See Guide
provides adequate lubrication for component performance.
G127 for discussion of cleaning agent and procedure selection.
Oxygen-compatible lubricants often have markedly different
lubricating properties from conventional lubricants.
6. Interferences
6.4 Environment and Assembly Requirements:
6.1 Disassembly:
6.4.1 Equipment intended for oxygen service must be
6.1.1 It is imperative that oxygen systems be cleaned as
handled carefully during all phases of a cleaning procedure.
individual components or piece parts, preferably before assem-
The environment should be clean and dust-free. Nearby
bly. Assembled systems must be disassembled for cleaning if
grinding, welding, and sanding should be prohibited. Parts
construction permits. Flushing an assembled system can de-
should not be allowed to stand in the open unprotected after
posit and concentrate contaminants in stagnant areas. Nonvola-
they have been cleaned. Care should be taken to avoid
tile cleaning agents may remain in trapped spaces and later
contamination by oil deposits from rotating machinery or oil
react with oxygen. Cleaning solutions may degrade nonmetals
aerosols in the air. Do not touch part surfaces that will be in
in an assembly. Caustic and acid cleaning solutions may cause
direct oxygen service except with clean gloves or handling
crevice corrosion in assemblies.
devices.
6.1.2 Manufactured products (that is, valves, regulators, and
6.4.2 In some cases, laminar-flow clean rooms may be
pumps) should be cleaned preferably by the manufacturer
necessary in which the entire room is purged with filtered air.
before final assembly and test.All tests should be structured to
In horizontal flow clean rooms, parts are cleaned and verified
prevent recontamination. The part must then be packaged in
in a sequence in which successive cleaning operations are at
oxygen-compatible materials (see 12.1) and identified to pro-
locations progressively closer to the filtered air source so that
tect it from contamination in transit and storage.The purchaser
the part and the environment each become steadily cleaner. In
shouldapprovethecleaningprocedureandpackagingtoassure
laminar vertical flow clean rooms, the layout of the successive
that they satisfy system requirements. Some purchasers may
cleaning operations is not as critical. See ISO 14664 for further
require the product manufacturer to certify cleanliness level
information.
and oxygen compatibility of all component materials.
6.1.3 Manufactured products cleaned by the purchaser must
7. Conditioning
be disassembled for cleaning if construction permits. The
7.1 Factors to consider before selecting cleaning methods
purchaser should follow the manufacturer’s instructions for
include:
disassembly, inspection for damage, reassembly, and testing.
7.1.1 Type of contaminant, that is, inorganic, organic,
6.2 Cleaners:
particulate, film, or fluid,
6.2.1 Mechanical cleaning methods such as abrasive 7.1.2 Base material or coating of the part to be cleaned,
blasting, tumbling, grinding, and wire brushing are very 7.1.3 Initial condition of the part to be cleaned,
aggressive and should be avoided on finished machined ar- 7.1.4 Required final cleanliness of the part,
G93/G93M − 19
7.1.5 Environmental impact and lawful disposition of haz- 8.2.1.3 Take care to minimize removal of the component
ardous waste products generated by the required cleaning parent material. This cleaning method may not be suitable for
method, solutions, and reagents used, components or systems with critical surface finishes or dimen-
sional tolerances.
7.1.6 Cost effectiveness of the required cleaning method,
8.2.1.4 In some cases, abrasive blast cleaning will induce
7.1.7 Effects of the selected cleaning methods on the part to
residual compressive stresses in the surfaces of metallic
be cleaned, such as mechanical, chemical, and thermal, and
components.Although this induced stress is beneficial in terms
7.1.8 Ease of cleaning (part configuration).
of fatigue strength, it may be detrimental to another of these
component’s material properties, such as magnetic and electri-
8. Cleaning Methods
cal characteristics.
8.1 General:
NOTE 2—Warning—Protective gloves, aprons, face shields, and respi-
8.1.1 Acleaning method is the procedure(s) used to bring a
ratory equipment are recommended unless the blast cleaning is performed
cleaning agent into contact with all component surfaces to be
inside a glove-box. The immediate health hazards are imbedding of stray
abrasive particles in eyes and skin. The long-term hazard could include
cleaned, with the goal of removing contaminants. Cleaning
respiratory disorders caused by inhalation of fine particles.
materials and equipment for use in oxygen-enriched environ-
ments should begin with disassembly to the elemental or
8.2.2 Wire Brush or Grinding Cleaning:
piece-part level as discussed in 6.1. When the component has
8.2.2.1 Wire brushing or grinding methods generally incor-
been disassembled, parts should be grouped according to
porate a power-driven wire or nonmetallic fiber-filled brush, or
cleaning method. While the methods described apply to most
an abrasive wheel. These are used to remove excessive scale,
metals, special precautions must be taken for nonmetals, which
weld slag, rust, oxide films, and other surface contaminants.
require special attention as discussed in 6.2.1 and 6.2.2.
Wirebrushesmaybeuseddryorwet.Thewetconditionresults
8.1.2 Cleaning methods can be categorized as mechanical, when the brushes are used in conjunction with alkaline
chemical, or both. Some cleaning operations are enhanced by
cleaning solutions or cold water rinses.
combining mechanical and chemical methods, such as me-
8.2.2.2 These mechanical methods may imbed brush or
chanical agitation of a chemical solution.
grinding material particles in the cleaning surface. Cleaning
brush selection depends on the component or system parent
NOTE 1—Warning—Both caustic and acid cleaning involve the use of
material.Nonmetallicbrushesaresuitableformostmaterialsto
hazardous materials and solutions. Full protective clothing, including
be cleaned. Carbon steel brushes should not be used on
gloves and face protection, should be worn by cleaning operators.
Disposal of spent cleaning solutions should be conducted according to
aluminum, copper, and stainless steel alloys.Any wire brushes
federal, state, and local regulations. The appropriate MSDS for the
previously used on carbon steel components or systems should
material must be reviewed and controls implemented before using
not be subsequently used on aluminum or stainless steel. The
hazardous materials.
usershouldbeawarethatwirebrushingandgrindingcanaffect
8.2 Mechanical Cleaning—These methods use mechani-
dimensions, tolerances, and surface finishes.
cally generated forces to remove contaminants from compo-
8.2.3 Tumbling—Sometimes called Barrel or Mass
nents. Examples of mechanical cleaning methods are abrasive
Cleaning, this procedure involves rolling or agitation of parts
blasting, grinding, tumbling, swabbing, and ultrasonication.
within a rotating barrel or vibratory tubs containing abrasive or
Details of these and other methods are discussed below.
cleaning solution. The container action, rotation, or vibration
8.2.1 Abrasive Blast Cleaning:
imparts relative motion between the components to be cleaned
and the abrasive medium or cleaning solution. This method
8.2.1.1 Abrasive blast cleaning involves the forceful im-
may be performed with dry or wet abrasives.The part size may
pingement of abrasive particles against surfaces to be cleaned
vary from a large casting to a delicate instrument component,
to remove scale, rust, paint, and other foreign matter. The
but mixing different components in one barrel should be
abrasive may be either dry or suspended in liquid. Various
avoided, as damage may occur from one component impacting
systems are used to propel abrasives, including airless abrasive
on another of a different type. Barrel cleaning may be used for
blast blades or vane-type wheels, pressure blast nozzles, and
descaling, deburring, burnishing, and general washing. Some
suction (induction) blast nozzles. Propellant gases should be
factors to consider in barrel cleaning are component size and
verified as oil-free.
shape, type and size of abrasive, load size, barrel rotational
8.2.1.2 Typical abrasive particle materials include metallic
speed, and ease of component/abrasive separation.
grit and shot, natural sands, manufactured oxide grit, carbide
8.2.4 Swab, Spray, and Dip Cleaning—Each of these meth-
grit, walnut shells, and glass beads. The specific abrasive
ods of applying cleaning solutions to the component surfaces
particle material used should be suitable for performing the
has its particular advantages. Swabbing is generally used on
intended cleaning without depositing contaminants that cannot
parts or components to clean small select areas only. Spraying
be removed by additional operations, such as high velocity
and dipping are used for overall cleaning. These methods are
blowing, vacuuming, and purging.
generally used with alkaline, acid, or solvent cleaning methods
discussed in later sections.
8.2.5 Vacuuming and Blowing—These methods remove
For a more detailed discussion of abrasive blast cleaning, see Metals Handbook
contaminants from the component by currents of clean, dry,
Desk Edition, 2nd Edition, Joseph R. Davis, Editor, American Society for Metals,
Metals Park, OH, 1999. oil-free air or nitrogen. These methods may be used to remove
G93/G93M − 19
loose dirt, slag, scale, and various particles, but they are not detergent flows to maximize efficiency of the detergent’s
suitable for removing surface oxides, greases, and oils. chemical action, the steam heat effect, and the steam jet’s
scrubbing action.
8.2.6 “Pig” Cleaning—Long continuous pipelines can be
8.3.4 Caustic and Detergent Cleaning—This method relates
cleaned in situ using “pigs,” piston-like cylinders with periph-
tothecleaningofvessels,pipingsystems,orcomponentseither
eral seals that can be pushed through a pipeline using com-
externally or internally and uses water as the primary solvent.
pressed gas pressure, typically nitrogen. Pigs may be equipped
Synthetic detergents and surfactants are combined with addi-
withscrapersorwirebrushes,andpairsofpigsmaycarryslugs
tives such as pH buffers, inhibitors, saponifiers, emulsifiers,
of liquid cleaning agents between them. Hence, a train of four
antifoaming agents, wetting agents, and others for beneficial
pigs can transport three isolated slugs of solution through a
effects.
pipeline to produce various levels of cleaning and rinsing. The
8.3.4.1 Caustic cleaning uses highly alkaline solutions to
mechanical and chemical suitability of the solvents, scrapers,
remove organic contamination such as hydrocarbon oils,
andwirebrushesshouldbeensuredasdetailedin8.2.2and8.3.
grease, and waxes. Some common alkaline salts available for
8.2.7 Ultrasonic Cleaning—Ultrasonic energy can be used
caustic cleaning are listed in
Table 2. Prepared solutions can be
with a variety of chemical cleaning agents to effect intimate
used in static tanks or vessels for component immersion.
contact between the part and the cleaning agent. Ultrasonic
Alternatively, solutions can be pumped or jetted onto or
agitationaidsremovaloflightlyadheredorembeddedparticles
through components. Depending on the detergent used, solu-
from solid surfaces. It is generally used in solvent cleaning of
tions may be alkaline, nontoxic, biodegradable, or noncorro-
small parts, precious metal parts, and components requiring a
sive. Some detergents may be toxic or corrosive, and detergent
very high degree of cleanliness. See Practice G131 for an
properties should be verified by the manufacturer or supplier.
ultrasonic cleaning procedure.
See Guide G127 for selection criteria. The cleaning solution
can be applied by spraying, immersing, or hand swabbing.
8.3 Aqueous Cleaning:
Normally, caustic cleaning solutions are applied at tempera-
8.3.1 The following methods are based on achieving an
tures up to 180 °F [82.2 °C]. It is important that the cleaning
interaction between the cleaning solution and the contaminant
solution reach all areas of the part to be cleaned. The cleaning
or component surface to effect easy removal of contaminant by
solution can be reused until it becomes ineffective as deter-
subsequent mechanical methods. The interaction may involve
mined by pH or contaminant concentration analysis. Experi-
surface activation, contaminant breakdown, oxide conversion,
ence may establish a contaminant level of the cleaning solution
and hydrophobic or hydrophilic transformations. Water used
above which a surface cannot be acceptably cleaned.
for dilution and rinsing of chemical cleaning agents must be as
cleanorcleanerthanthelevelofcleanlinessdesiredandfreeof
NOTE 3—Caution: Alkalai cleaners attack aluminum.
contaminants to prevent reactions with the cleaning agents.
8.3.4.2 Aqueous systems have few problems with worker
Water shall be of a grade equal or better to that specified in
safety compared to most other solvents. They are not flam-
Specification D1193,Type II, without the silica analysis.Water
mable or explosive, and toxicity is low for most formulations.
with a higher specific resistance may be required for particular
Aqueous systems can be designed to remove particulate and
applications or cleaning systems.
film contamination. They are especially good for removing
8.3.2 Hot-Water Cleaning—Hot water cleaning removes
inorganic or polar materials. Aqueous cleaning functions by
gross organic and particulate contamination from parts by
several mechanisms other than solvency, including
using low to moderate heat, detergent, and some mechanical
saponification, displacement, emulsification, and dispersion.
agitation. Equipment used during hot-water cleaning may
Ultrasonics are especially suited for aqueous solvents.
consist of a spray system or a cleaning vat with or without
8.3.4.3 The part must be thoroughly rinsed to prevent the
suitable agitation of the solution. Hot-water cleaning with
cleaning solution and contaminants from redepositing on the
detergent can be used where steam is not required to free and
surface. The surface must not be allowed to dry between the
fluidize contaminants. Consideration should be given to the
cleaning and rinsing phases. Frequently, some type of water
size, shape, and number of parts to ensure adequate contact
rinsing helps to remove the cleaning solution and aids in the
between part surfaces and the solution. Solution temperature
drying process. Parts with small crevices and blind channels
shouldbeasrecommendedbythecleaningagentmanufacturer.
Water-soluble contaminants are best removed by prompt flush-
TABLE 2 Common Alkaline Salts (see 8.3.4.1 and 9.4)
ing with sufficient quantities of hot or cold clean water before
A
IUPAC Name Formula Common Name
the cleaning agents have time to precipitate. The parts are then
Sodium hydroxide NaOH Caustic soda
dried by blowing with dry oil-free air or nitrogen, which may
Lye
be heated to shorten the drying time.
Sodium metasilicate Na SiO Sodium silicate
2 2
Water glass
8.3.3 Steam Cleaning—Steam cleaning removes organic
Sodium carbonate Na CO Soda ash
2 3
and particulate contaminants from parts by using pressure,
Sodium tetraborate decahydrate Na B O ·10H O Borax
2 4 7 2
Sodium orthophosphate Na PO ·12H O Trisodium phosphate (TSP)
heat,andsometimesdetergents.Someorganicsareremovedby
2 4 2
Sodium phosphate tribasic
decreasing their viscosity, or “thinning” them with steam heat.
Sodium pyrophosphate Na P O ·10H O Tetrasodium pyrophosphate
4 2 7 2
Detergent may be added to disperse and emulsify organics,
Sodium polyphosphate
which allows rinsing of the contaminant by condensed steam. A
According to the International Union of Pure and Applied Chemistry.
The system should provide control over steam, water, and
G93/G93M − 19
TABLE 3 Alkaline Chemical Cleaning Materials (see 8.3.4.3)
A B,C
Metal Reason for Cleaning Cleaning Chemicals Other Treatment
Carbon and low alloy steels Removal of heavy soil, grease, and oil Mixtures of sodium hydroxide, Solutions should not be allowed to dry on
carbonates, phosphates and silicates, the part and must be thoroughly rinsed
and synthetic wetting agents
Austenitic stainless steel Removal of heavy soil, grease, light oils, Mixtures of sodium hydroxide,
and cutting fluid carbonates, phosphates and silicates,
and synthetic wetting agents
Copper and alloys Removal of grease, lubricating oil, Mixtures of sodium hydroxide, Usually bright dipped in dichromate acid
drawing compound, oxide, metallic polyphosphates, silicates, carbonates, solution
particles, or other contaminants and wetting agents
Removal of brazing flux Hot water
Aluminum and alloys Removal of grease, oil, and oxide Sodium hydroxide, sodium phosphate, Dilute nitric acid dip to remove smut
and sodium carbonate for etching
Sodium carbonate, sodium silicate,
sodium pyrophosphate, and sodium
metasilicate for nonetching
A
The manufacturer’s specification for application of the cleaning agent shall be strictly enforced.
B
Postchemical Cleaning Treatment—After cleaning using alkaline chemicals, all components shall be thoroughly rinsed, preferably using hot flowing water to aid drying,
unless otherwise specified by the cleaning material supplier. Some components require treatment by using neutralizing solutions after certain cleaning treatments.
C
Thorough rinsing is necessary to avoid stress corrosion risk.
may be difficult to clean because of the relatively high surface achieved by purging with a clean, flowing, dry gas, usually
tension and capillary forces of water-based cleaners. Some nitrogen or air. Care must be taken in measuring the dew point
aqueouscleanerresiduescanbedifficulttorinsefromsurfaces; of a flowing gas. It is possible to inadvertently measure the
nonionic surfactants are especially difficult to rinse. A method dryness of the purge gas only. To sample correctly, a lock-up
of determining when rinsing is complete is to monitor the used andpressurizationprocedure,withatimeallowanceinterval,is
rinse water until a pH of 60.2 of the starting water pH is necessary.Itemsdriedwithaflowing,heated,drygaspurgeare
achieved. Parts with complex geometries may be difficult to usually considered dry when the dew point of the exit gas is
dry. Clean, dry, oil-free air or nitrogen, heated if necessary, within 5 °F [3 °C] of the purge gas.
may be used for drying.Alternatively, vacuum may be used to (4) Dryness is measured in many ways:
achieve desired dryness. Table 3 gives general recommenda- (a) Relative humidity,
tionsforalkalinecleaning.Thistableliststhemetallicmaterial, (b) Dew point,
type of contaminant to be removed, and the alkaline solution (c) Unit mass of water per unit mass of gas (ppm),
used. (d) Unit volume of water per unit volume of gas (v/v),
8.3.4.4 Drying: and
(1) When aqueous cleaning is used on oxygen system (e) Moles of water per moles of air.
components, rinsing and drying are of critical concern. Drying (5) Oxygen systems are typically considered dry at equi-
is the removal of water or other solvents from critical surfaces. librium exit gas dew points of from 0 °F [-18 °C] to as low as
The actual process of drying involves a change of state and -70 °F [-57 °C] depending on the specific application. The
requires energy. The amount of energy depends on many choice depends on many variables such as cost, time, use
factors such as the solvent to be evaporated, the configuration temperature, and effects of moisture on components. Industrial
of the hardware, the temperature of the operation, and the gases are easily obtained with dew points of -40 °F [-40 °C], a
conductivity of the liquid and the hardware. The heat of common specification level for oxygen system dryness.
vaporizationforwaterisanorderofmagnitudehigherthanthat 8.3.5 Semiaqueous Cleaning:
forsomecommonchlorofluorocarbonsolvents.Theremovalof 8.3.5.1 Semiaqueous cleaning uses hydrocarbon-water
vapor is also critical in drying, and a means for removal of emulsions to remove heavy contaminants from part surfaces
vapor must be provided. This is usually accomplished with a with organic solvents dispersed in an aqueous medium by an
moving dry gas purge. emulsifying agent. The cleaning action of emulsion cleaners
(2) In selection of a drying process, consideration must be combines the advantages of both the aqueous and organic
giventothelevelofdrynessrequired.Theusershouldevaluate phases.
each method for the specific application intended. There are (1) Many emulsion cleaners are commercially available
three basic water removal methods commonly used: and are composed of petroleum-derived solvents and surfac-
(a) Physical—actual removal of liquid such as scraping, tants that render them emulsifiable. Some emulsion cleaners
wiping, centrifuging, or blowing. tend to separate into individual solutions if left standing for
(b) Solvent—wettingthepartwithahighervaporpressure extended periods, and it may be necessary to periodically
liquid to displace the water, such as with alcohol or hydrofluo- agitate them so that they remain emulsified. It is important that
rocarbons. two-part mixtures are not allowed to separate, to preclude only
(c) Evaporation—adding energy and physically removing part of the mixture being removed from the system. Emulsion
the vapor such as drying by oven, air, or purge. cleaners are normally applied to parts by soaking, spraying, or
(3) Small- and medium-size hardware drying is often done swabbing. Emulsion cleaners must be removed by rinsing and
in filtered gas-purged ovens. System and tank drying may be subsequent cleaning operations.
G93/G93M − 19
8.3.5.2 One type of semiaqueous material is a water emul- prevent harmful attacks on base metals. Hydrochloric acid
sion with natural citrus and pine-based terpenes. Semiaqueous should not be used on stainless steel since it may cause stress
cleaners are either emulsified in water and applied in a manner corrosion or stress corrosion cracking.
similar to standard aqueous cleaners or they are applied in 8.3.6.4 Chromic and nitric acid cleaning compounds are
concentrated form and then rinsed with water. Semiaqueous recommendedforaluminumandcopperandtheiralloys.These
formulations are compatible with most metals and plastics. compounds are not true cleaning agents, but are used for
They have good cleaning ability, especially for heavy grease, deoxidizing, brightening, and for removing black residue that
tar, wax, and hard to remove soils. The semiaqueous formula- forms during cleaning with an alkaline solution. Some com-
tions are considered nonflammable in bulk but can be flam- pounds are available as liquids, and others as powders. They
mable as a mist. Proper equipment design is essential to are mixed in concentrations of 5 to 50 % in water, depending
minimize risk from flammable mists. Some formulations can on the cleaning agent and the amount of oxide or scale to be
auto-oxidize into an undesirable condition. Material must be removed.
verified with the supplier. 8.3.6.5 Acid cleaning requires a storage or an immersion
8.3.5.3 The cleaning solution must be thoroughly rinsed tank, recirculation pump, associated piping, and valving com-
from the part to prevent contaminants from redepositing on the patiblewiththecleaningsolution.Commontechniquesforacid
surface. The surface must not be allowed to dry between the cleaningareimmersion,swabbing,andspraying.Acidcleaning
cleaning and rinsing phases. Semiaqueous residues are espe- compounds should not be used unless their application and
cially difficult to rinse from surfaces.Amore thorough analysis performance are known or are discussed with the cleaning
than rinse water pH may be required to determine rinse phase compound manufacturer. The manufacturer’s recommenda-
completion. Parts with complex geometries may be difficult to tions regarding concentration and temperature should be fol-
dry. Clean, dry, oil-free air or nitrogen, heated if necessary, lowed for safe handling of the cleaning agent. After acid
may be used for drying. Alternatively, vacuum may be com- cleaning, surfaces must be thoroughly rinsed with water equal
bined with purging to achieve desired level of dryness. Care to that described in 8.3.1 to remove all traces of acid and then
must be used to prevent buckling from external pressure when thoroughly dried after the final water rinse. To minimize
vacuum is applied. staining, do not allow surfaces to dry between successive steps
8.3.6 Acid Cleaning: of the acid cleaning and rinsing procedure. A neutralizing
8.3.6.1 Acid cleaning is a process in which a solution of treatment may be required under some conditions. Neutraliza-
mineral acid, organic acid, or acid salt (often in combination tion must be followed by repeated water rinsing to remove all
with a wetting agent and detergent) is used to remove oxides, traces of the neutralizing agent. If drying is required, it can be
oils, and other contaminants from parts, with or without the completedwithheatedorunheated,dry,oil-freeairornitrogen.
application of heat.Acid cleaning must be carefully controlled Table 4 gives typical acid solutions for cleaning various types
to avoid damage to the part surfaces, such as undesired etching of metallic materials.
or pickling.The type of cleaning agent selected will depend on 8.3.7 Solvent Cleaning—This cleaning or degreasing
the material or part to be cleaned. The following is a general method was once considered to be the principal procedure for
guide for the use of acid cleaning. removal of soluble organic contaminants from components to
8.3.6.2 Phosphoric acid cleaning agents can be used for be used in oxygen service and was suitable for use with most
most metals. These agents will remove oxides, light rust, light metals. The use and attractiveness of chlorinated solvents as
soils, and fluxes. cleaningsolutions,however,havebeenlimitedbyenvironmen-
8.3.6.3 Hydrochloricacidcleaningagentsarerecommended tal concerns and legislative restrictions. Chlorinated solvents
only for carbon and low alloy steels. These agents will remove are being replaced by aqueous or semiaqueous detergents or
rust, scale, and oxide coatings and will strip chromium, zinc, emulsion solutions, often in conjunction with deionized water
and cadmium platings. Certain acidic solutions, including as part of the process. Alcohols, ethers, and other specialized
hydrochloric or nitric acids, should contain an inhibitor to solvents are used in unique cleaning applications where their
TABLE 4 Acid Chemical Cleaning Materials (see 8.3.6.5)
A B
Metal Reason for Cleaning Cleaning Chemicals Other Treatment
Carbon and low alloy steels Removal of scale and oxide films Hydrochloric or sulfuric acid and wetting Dilute alkali dip to neutralize acid
(pickling) agents or treatment with inhibitor
Removal of light rust Citric, sulfuric, and phosphoric acids Light scrubbing action helpful
Removal of grease, oil, or drawing Phosphoric acid and synthetic detergents
compound mixture
Cast iron Removal of oxide Chromic and sulfuric acid
Austenitic stainless steels Removal of oxide, tarnish and scale and Chromic, sulfuric, and hydrofluoric acid, or Nitric acid solution used to
metallic deposits/contaminants nitric, hydrofluoric, and phosphoric acids brighten
Copper and alloys Removal of scale and oxide (pickling) Hydrochloric or sulfuric acid
Brightening Sulfuric, nitric, and hydrochloric acids
Aluminum and alloys Removal of oxide (etch cleaning) Nitric acid solution used to brighten Hydroxide solutions
A
The manufacturer’s specification for application of the cleaning agent should be strictly observed or the properties of the metals can be impaired. Time, temperature, and
concentrations are very important.
B
Postchemical Cleaning Treatment—After acid cleaning, all components should be thoroughly rinsed, preferably using flowing hot water to aid drying, unless otherwise
specified by the cleaning material supplier. Some components require treatment with neutralizing solutions after certain cleaning treatments.
G93/G93M − 19
hazards are warranted due to process restrictions. A list of heat source higher than 392 °F [200 °C] should be prohibited
common solvents appears in 11.4.2 and Table 5. This method in the vicinity of solvent vapor. Exposure of the solvent to
is limited by the ability of the solvent to reach and dissolve any daylight over a prolonged period may cause decomposition.
contaminants present. Before starting any cleaning operation, a
8.3.8.4 Solvent containers should not be left in working
reference sample of fresh clean solvent should be set aside to
areas without suitable securely fitted lids or caps. Skin contact
use as a base reference.At intervals throughout the procedure,
should be avoided by wearing protective clothing. Solvents
samples of used solvent can be compared with the reference
should be carried only if contained in suitable properly labeled
sample to determine the level of contamination. Methods of
containers.
determining contamination can be by comparison to the color
8.3.8.5 Federal, state, local, or insurance regulations may
ofthereferencesample,byfluorescenceunderultravioletlight,
require that precautions such as electrically grounding
byanalysis,orbyevaporation.Cleanglassbottlesmustbeused
containers, remote storage, and spill containment structures be
to hold samples.
provided. Some solvents are flammable, toxic, or carcinogenic,
8.3.7.1 Aftercompletionofanysolventcleaningmethod,all
and manufacturer’s recommended safety precautions should be
gross residual cleaning fluid must be drained from the compo-
followed. Also, compliance to federal, state, and local regula-
nent to prevent drying in pools. The component shall then be
tions may be required. Manufacturers of ultrasonic cleaning
purgedanddriedwithheateddry,oil-freeairornitrogen.Small
tanks and associated equipment issue recommendations on
components may be air dried if appropriate, so long as they do
their safe operation. Operators shall comply with the manufac-
not become recontaminated.
turer’s recommendations. A material Safety Data Sheet is
8.3.7.2 Solvent cleaning may be performed using any of the
required for each chemical used.
methods previously discussed such as swabbing and spraying.
NOTE 4—Warning—Aluminum and its alloys have been known to
Components and disassembled parts can also be cleaned by
react vigorously with chlorinated hydrocarbon solvents to produce hydro-
immersion in a solvent tank and applying agitation. The
chloricacidvapor,whichisbothtoxicandcorrosive.Theconditionsunder
process can be improved by the use of ultrasonic cleaning
which these reactions occur are not well known. This particularly occurs
techniques. Cleaning by forced circulation of a liquid solvent
on aluminum particles such as swarf or chips from machining or cutting
processes.
flow through the component can also be carried out. The
duration of cleaning by circulation shall be continued using
8.3.8
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: G93 − 03 (Reapproved 2011) G93/G93M − 19
Standard PracticeGuide for
Cleaning Methods and Cleanliness Levels for Materialand
Cleaning Methods for Materials and Equipment Used in
Oxygen-Enriched Environments
This standard is issued under the fixed designation G93;G93/G93M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers the selection of methods and apparatus for cleaning materials and equipment intended for service in
oxygen-enriched environments. Contamination problems encountered in the use of enriched air, mixtures of oxygen with other
gases, or any other oxidizing gas may be solved by the same cleaning procedures applicable to most metallic and nonmetallic
materials and equipment. Cleaning examples for some specific materials, components, and equipment, and the cleaning methods
for particular applications, are given in the appendices.
1.2 This practice includes levels of cleanliness used for various applications and the methods used to obtain and verify these
levels.
1.3 This practice applies to chemical-, solvent-, and aqueous-based processes.
1.4 This practice describes nonmandatory material for choosing the required levels of cleanliness for systems exposed to oxygen
or oxygen-enriched atmospheres.
1.5 This practice proposes a practical range of cleanliness levels that will satisfy most system needs, but it does not deal in
quantitative detail with the many conditions that might demand greater cleanliness or that might allow greater contamination levels
to exist. Furthermore, it does not propose specific ways to measure or monitor these levels from among the available methods.
1.6 The values stated in both inch-pound and SI units are to be regarded separately as the standard unit. The values given in
parentheses are for information only.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. Federal, state and local safety and disposal regulations concerning the particular hazardous materials,
reagents, operations, and equipment being used should be reviewed by the user. The user is encouraged to obtain the Material
Safety Data Sheet (MSDS) from the manufacturer for any material incorporated into a cleaning process. Specific cautions are given
in Section 8.
2. Referenced Documents
2.1 ASTM Standards:
A380 Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems
D1193 Specification for Reagent Water
E312 Practice for Description and Selection of Conditions for Photographing Specimens Using Analog (Film) Cameras and
Digital Still Cameras (DSC) (Withdrawn 2017)
E1235 Test Method for Gravimetric Determination of Nonvolatile Residue (NVR) in Environmentally Controlled Areas for
Spacecraft
E2042 Practice for Cleaning and Maintaining Controlled Areas and Clean Rooms
F312 Test Methods for Microscopical Sizing and Counting Particles from Aerospace Fluids on Membrane Filters
This practiceguide is under the jurisdiction of ASTM Committee G04 on Compatibility and Sensitivity of Materials in Oxygen Enriched Atmospheres and is the direct
responsibility of Subcommittee G04.02 on Recommended Practices.
Current edition approved April 1, 2011Oct. 1, 2019. Published April 2011 October 2019. Originally approved in 1987. Last previous edition approved in 20032011 as
G93 – 03e01.G93 – 03(2011). DOI: 10.1520/G0093-03R11.10.1520/G0093_G0093M-19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G93/G93M − 19
F331 Test Method for Nonvolatile Residue of Solvent Extract from Aerospace Components (Using Flash Evaporator)
G63 Guide for Evaluating Nonmetallic Materials for Oxygen Service
G88 Guide for Designing Systems for Oxygen Service
G121 Practice for Preparation of Contaminated Test Coupons for the Evaluation of Cleaning Agents
G122 Test Method for Evaluating the Effectiveness of Cleaning Agents
G125 Test Method for Measuring Liquid and Solid Material Fire Limits in Gaseous Oxidants
G127 Guide for the Selection of Cleaning Agents for Oxygen-Enriched Systems
G128 Guide for Control of Hazards and Risks in Oxygen Enriched Systems
G131 Practice for Cleaning of Materials and Components by Ultrasonic Techniques
G136 Practice for Determination of Soluble Residual Contaminants in Materials by Ultrasonic Extraction
G144 Test Method for Determination of Residual Contamination of Materials and Components by Total Carbon Analysis Using
a High Temperature Combustion Analyzer
2.2 CGA Documents:
CGA Pamphlet G-4.1 Cleaning Equipment for Oxygen Service
CGA Pamphlet G-4.4 Industrial Practices for Gaseous Oxygen Transmission and Distribution Piping Systems
2.3 SAE Document:
ARP 598 The Determination of Particulate Contamination in Liquids by the Particle Count Method
2.4 ISO Document:
ISO 14644-1 Cleanrooms and Associated Controlled Environments—Part 1: Classification of Air Cleanliness
3. Terminology
3.1 Definitions:
3.1.1 contaminant, n—unwanted molecular or particulate matter that could adversely affect or degrade the operation, life, or
reliability of the systems or components upon which it resides.
3.1.2 contamination, n—(1) the amount of unwanted molecular or particulate matter in a system; (2) the process or condition
of being contaminated.
3.1.2.1 Discussion—
Contamination and cleanliness are opposing properties; increasing cleanliness implies decreasing contamination.
3.1.3 direct oxygen service, n—service in contact with oxygen-enriched atmosphere during normal operation.
3.1.3.1 Discussion—
Examples are oxygen compressor piston rings or control valve seats.
3.1.4 nonmetal, n—any material other than a metal, nonpolymeric alloy, or any composite in which the metallic component is
not the most easily ignited component and for which the individual constituents cannot be evaluated independently, including
ceramics (such as glass), synthetic polymers (such as most rubbers, thermoplastics, and thermosets), and natural polymers (such
as naturally occurring rubber, wood, and cloth). Nonmetallic is the adjective use of this term.
3.1.5 oxygen compatibility (also oxidant compatibility), n—the ability of a substance to coexist with both oxygen and a potential
source(s) of ignition at an expected pressure and temperature with a magnitude of risk acceptable to the user.
3.1.6 qualified technical personnel, n—persons such as engineers and chemists who, by virtue of education, training, or
experience, know how to apply physical and chemical principles involved in the reactions between oxidants and other metals.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 cleanliness, n—the degree to which an oxygen system is free of contaminant.
3.2.2 fibers, n—particulate matter with a length of 100 μm or greater, and a length-to-width ratio of 10 to 1 or greater.
3.2.3 particulate, n—a general term used to describe a finely divided solid of organic or inorganic matter.
3.2.3.1 Discussion—
These solids are usually reported as the amount of contaminant by the population of a specific micrometer size. See methods
described in Methods F312 or ARP 598 for particle size and population determination.
Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5th Floor, Chantilly, VA 20151-2923, http://www.cganet.com.
Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale, PA 15096-0001, http://www.sae.org.
Available from International Organization for Standardization (ISO), 1, ch. de la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://www.iso.ch.
G93/G93M − 19
4. Summary of Practice
4.1 General methods, apparatus, and reagents for cleaning materials and equipment used in oxygen-enriched environments are
described in this practice. Exact procedures are not given because they depend on the contaminant type and material to be cleaned,
cleaning agent used, and degree of cleanliness required. Methods may be used individually, or may be combined or repeated to
achieve the desired results. Examples of cleaning procedures that have been successfully used for specific materials, components,
and equipment in selected applications are described in the appendices. An index of the specific materials, components, equipment,
and applications covered in these examples is given in Table X1.1.
4.2 For the purpose of this practice, both solid and fluid contaminants have been subclassed into three categories: organics,
inorganics, and particulates. A list of common contamination levels is given in Table 1.
4.3 Cleanliness specifications that have been used in the past are identified, levels of cleanliness that can be achieved are listed
along with factors that suggest potential upper limits for allowable system contamination, and the practical difficulties in adopting
and achieving adequately clean systems are reviewed. Cleanliness specifications used by suppliers and manufacturers often differ;
it is therefore important to communicate and agree upon which specification is to be used for a given system and to adhere to the
most conservative measures.
5. Significance and Use
5.1 The purpose of this practice is to furnish qualified technical personnel with pertinent information for the selection of
cleaning methods for cleaning materials and equipment to be used in oxygen-enriched environments. This practice furnishes
qualified technical personnel with guidance in the specification of oxygen system cleanliness needs. It does not actually specify
cleanliness levels.
5.2 Insufficient cleanliness of components used in oxygen systems can result in the ignition of contaminants or components by
a variety of mechanisms such as particle, mechanical, or pneumatic impact. These mechanisms are explained in detail in Guide
G88.
5.3 Adequate contamination control in oxygen systems is imperative to minimize hazards and component failures that can result
from contamination. Contamination must also be minimized to ensure an acceptable product purity.
5.4 Removal of contaminants from materials and components depends on system configuration, materials of construction, and
type and quantity of contaminant.
5.5 Examples of cleaning procedures contained herein may be followed or specified for those materials, components, and
equipment indicated. The general cleaning text can be used to establish cleaning procedures for materials, components, equipment,
and applications not addressed in detail. See Guide G127 for discussion of cleaning agent and procedure selection.
6. Interferences
6.1 Disassembly:
6.1.1 It is imperative that oxygen systems be cleaned as individual components or piece parts, preferably before assembly.
Assembled systems must be disassembled for cleaning if construction permits. Flushing an assembled system can deposit and
concentrate contaminants in stagnant areas. Nonvolatile cleaning agents may remain in trapped spaces and later react with oxygen.
Cleaning solutions may degrade nonmetals in an assembly. Caustic and acid cleaning solutions may cause crevice corrosion in
assemblies.
6.1.2 Manufactured products (that is, valves, regulators, and pumps) should be cleaned preferably by the manufacturer before
final assembly and test. All tests should be structured to prevent recontamination. The part must then be packaged in
oxygen-compatible materials (see 12.1) and identified to protect it from contamination in transit and storage. The purchaser should
approve the cleaning procedure and packaging to assure that they satisfy system requirements. Some purchasers may require the
product manufacturer to certify cleanliness level and oxygen compatibility of all component materials.
A
TABLE 1 Oil Film Contamination Level Specifications
Concentration,
Source
2 2
mg/m (mg/ft )
0.14 (0.013) 1967 Navy Standard per Presti and DeSimone (1)
10.8 (1) NASA KSC 123 per Report MTB 306-71 (2)
16.1 (1.5) Recommended by Presti and DeSimone (1)
43.1 (4) Air Force 1950s value per LeSuer (3)
75.3 (7) Recommended by Walde (4)
108 (10 mg/ft or per item) Union Carbide Guideline (5,6)
50-100 (4.6 to 9.3) Compressed Gas Association Pamphlet G-4.8 (7)
50 to 100 (4.6 to 9.3) Compressed Gas Association Pamphlet G-4.8 (7)
500 (47.5) Compressed Gas Association Pamphlet G-4.1 (8)
A
The boldface numbers in parentheses refer to the list of references at the end of
this standard.
G93/G93M − 19
6.1.3 Manufactured products cleaned by the purchaser must be disassembled for cleaning if construction permits. The purchaser
should follow the manufacturer’s instructions for disassembly, inspection for damage, reassembly, and testing.
6.2 Cleaners:
6.2.1 Mechanical cleaning methods such as abrasive blasting, tumbling, grinding, and wire brushing are very aggressive and
should be avoided on finished machined articles. Such methods can damage sealing surfaces, remove protective coatings, and
work-harden metals. Sensitive surfaces must be protected before mechanical cleaning methods are applied.
6.2.2 Chemical cleaners, both acid and caustic, can damage metal parts if not neutralized upon completion of cleaning.
Corrosion, embrittlement, or other surface modifications are potentially harmful side effects of chemical cleaning agents. Crevice
corrosion can occur and sealing surfaces can be etched enough to destroy the finish necessary to seal the part. See Test Method
G122 and Guide G127 for methods used to evaluate cleaners for use on various materials used in oxygen service.
6.2.3 Solvent cleaning solutions often damage plastics and elastomers. The manufacturer should be consulted or sample parts
should be tested to ensure that the solvent is not harmful to the item being cleaned.
6.3 Lubricants:
6.3.1 Mechanical components are normally assembled with lubricants on seals, threads, and moving surfaces. The manufacturer
should be consulted to determine the kind of lubricant originally used on the article to ensure that the cleaning solutions and
methods selected are effective in removing the lubricant and will not damage the component.
6.3.2 Oxygen-compatible lubricants should be selected in accordance with Guide G63. The component manufacturer should
also be consulted to ensure that the selected lubricant provides adequate lubrication for component performance. Oxygen-
compatible lubricants often have markedly different lubricating properties from conventional lubricants.
6.4 Environment and Assembly Requirements:
6.4.1 Equipment intended for oxygen service must be handled carefully during all phases of a cleaning procedure. The
environment should be clean and dust-free. Nearby grinding, welding, and sanding should be prohibited. Parts should not be
allowed to stand in the open unprotected after they have been cleaned. Care should be taken to avoid contamination by oil deposits
from rotating machinery or oil aerosols in the air. Do not touch part surfaces that will be in direct oxygen service except with clean
gloves or handling devices.
6.4.2 In some cases, laminar-flow clean rooms may be necessary in which the entire room is purged with filtered air. In
horizontal flow clean rooms, parts are cleaned and verified in a sequence in which successive cleaning operations are at locations
progressively closer to the filtered air source so that the part and the environment each become steadily cleaner. In laminar vertical
flow clean rooms the layout of the successive cleaning operations is not as critical. See ISO 14664 for further information.
7. Conditioning
7.1 Factors to consider before selecting cleaning methods include:
7.1.1 Type of contaminant, that is, inorganic, organic, particulate, film, or fluid,
7.1.2 Base material or coating of the part to be cleaned,
7.1.3 Initial condition of the part to be cleaned,
7.1.4 Required final cleanliness of the part,
7.1.5 Environmental impact and lawful disposition of hazardous waste products generated by the required cleaning method,
solutions, and reagents used,
7.1.6 Cost effectiveness of the required cleaning method,
7.1.7 Effects of the selected cleaning methods on the part to be cleaned, such as mechanical, chemical, and thermal, and
7.1.8 Ease of cleaning (part configuration).
8. Cleaning Methods
8.1 General:
8.1.1 A cleaning method is the procedure(s) used to bring a cleaning agent into contact with all component surfaces to be
cleaned, with the goal of removing contaminants. Cleaning materials and equipment for use in oxygen-enriched environments
should begin with disassembly to the elemental or piece-part level as discussed in 6.1. When the component has been disassembled,
parts should be grouped according to cleaning method. While the methods described apply to most metals, special precautions must
be taken for nonmetals, which require special attention as discussed in 6.2.1 and 6.2.2.
8.1.2 Cleaning methods can be categorized as mechanical, chemical, or both. Some cleaning operations are enhanced by
combining mechanical and chemical methods, such as mechanical agitation of a chemical solution.
NOTE 1—Caution: Both caustic and acid cleaning involve the use of hazardous materials and solutions. Full protective clothing, including gloves and
face protection, should be worn by cleaning operators. Disposal of spent cleaning solutions should be conducted according to federal, state, and local
regulations. The appropriate MSDS for the material must be reviewed and controls implemented before using hazardous materials.
8.2 Mechanical Cleaning—These methods use mechanically generated forces to remove contaminants from components.
Examples of mechanical cleaning methods are abrasive blasting, grinding, tumbling, swabbing, and ultrasonication. Details of
these and other methods are discussed below.
G93/G93M − 19
8.2.1 Abrasive Blast Cleaning:
8.2.1.1 Abrasive blast cleaning involves the forceful impingement of abrasive particles against surfaces to be cleaned to remove
scale, rust, paint, and other foreign matter. The abrasive may be either dry or suspended in liquid. Various systems are used to
propel abrasives, including airless abrasive blast blades or vane-type wheels, pressure blast nozzles, and suction (induction) blast
nozzles. Propellant gases should be verified as oil-free.
8.2.1.2 Typical abrasive particle materials include metallic grit and shot, natural sands, manufactured oxide grit, carbide grit,
walnut shells, and glass beads. The specific abrasive particle material used should be suitable for performing the intended cleaning
without depositing contaminants that cannot be removed by additional operations, such as high velocity blowing, vacuuming, and
purging.
8.2.1.3 Take care to minimize removal of the component parent material. This cleaning method may not be suitable for
components or systems with critical surface finishes or dimensional tolerances.
8.2.1.4 In some cases, abrasive blast cleaning will induce residual compressive stresses in the surfaces of metallic components.
Although this induced stress is beneficial in terms of fatigue strength, it may be detrimental to another of these component’s
material properties, such as magnetic and electrical characteristics.
NOTE 2—Caution: Protective gloves, aprons, face shields, and respiratory equipment are recommended unless the blast cleaning is performed inside
a glove-box. The immediate health hazards are imbedding of stray abrasive particles in eyes and skin. The long-term hazard could include respiratory
disorders caused by inhalation of fine particles.
8.2.2 Wire Brush or Grinding Cleaning:
8.2.2.1 Wire brushing or grinding methods generally incorporate a power-driven wire or nonmetallic fiber-filled brush, or an
abrasive wheel. These are used to remove excessive scale, weld slag, rust, oxide films, and other surface contaminants. Wire
brushes may be used dry or wet. The wet condition results when the brushes are used in conjunction with alkaline cleaning
solutions or cold water rinses.
8.2.2.2 These mechanical methods may imbed brush or grinding material particles in the cleaning surface. Cleaning brush
selection depends on the component or system parent material. Nonmetallic brushes are suitable for most materials to be cleaned.
Carbon steel brushes should not be used on aluminum, copper, and stainless steel alloys. Any wire brushes previously used on
carbon steel components or systems should not be subsequently used on aluminum or stainless steel. The user should be aware
that wire brushing and grinding can affect dimensions, tolerances, and surface finishes.
8.2.3 Tumbling—Sometimes called Barrel or Mass Cleaning, this procedure involves rolling or agitation of parts within a
rotating barrel or vibratory tubs containing abrasive or cleaning solution. The container action, rotation, or vibration imparts
relative motion between the components to be cleaned and the abrasive medium or cleaning solution. This method may be
performed with dry or wet abrasives. The part size may vary from a large casting to a delicate instrument component, but mixing
different components in one barrel should be avoided, as damage may occur from one component impacting on another of a
different type. Barrel cleaning may be used for descaling, deburring, burnishing, and general washing. Some factors to consider
in barrel cleaning are component size and shape, type and size of abrasive, load size, barrel rotational speed, and ease of
component/abrasive separation.
8.2.4 Swab, Spray, and Dip Cleaning—Each of these methods of applying cleaning solutions to the component surfaces has its
particular advantages. Swabbing is generally used on parts or components to clean small select areas only. Spraying and dipping
are used for overall cleaning. These methods are generally used with alkaline, acid, or solvent cleaning methods discussed in later
sections.
8.2.5 Vacuuming and Blowing—These methods remove contaminants from the component by currents of clean, dry, oil-free air
or nitrogen. These methods may be used to remove loose dirt, slag, scale, and various particles, but they are not suitable for
removing surface oxides, greases, and oils.
8.2.6 “Pig” Cleaning—Long continuous pipelines can be cleaned in situ using “pigs,” piston-like cylinders with peripheral
seals that can be pushed through a pipeline using compressed gas pressure, typically nitrogen. Pigs may be equipped with scrapers
or wire brushes, and pairs of pigs may carry slugs of liquid cleaning agents between them. Hence, a train of four pigs can transport
three isolated slugs of solution through a pipeline to produce various levels of cleaning and rinsing. The mechanical and chemical
suitability of the solvents, scrapers, and wire brushes should be ensured as detailed in 8.2.2 and 8.3.
8.2.7 Ultrasonic Cleaning—Ultrasonic energy can be used with a variety of chemical cleaning agents to effect intimate contact
between the part and the cleaning agent. Ultrasonic agitation aids removal of lightly adhered or embedded particles from solid
surfaces. It is generally used in solvent cleaning of small parts, precious metal parts, and components requiring a very high degree
of cleanliness. See Practice G131 for an ultrasonic cleaning procedure.
8.3 Aqueous Cleaning:
8.3.1 The following methods are based on achieving an interaction between the cleaning solution and the contaminant or
component surface to effect easy removal of contaminant by subsequent mechanical methods. The interaction may involve surface
activation, contaminant breakdown, oxide conversion, and hydrophobic or hydrophilic transformations. Water used for dilution and
For a more detailed discussion of abrasive blast cleaning, see Metals Handbook Desk Edition, 2nd Edition, Joseph R. Davis, Editor, American Society for Metals, Metals
Park, OH, 1999.
G93/G93M − 19
rinsing of chemical cleaning agents must be as clean or cleaner than the level of cleanliness desired and free of contaminants to
prevent reactions with the cleaning agents. Water shall be of a grade equal or better to that specified in Specification D1193, Type
II, without the silica analysis. Water with a higher specific resistance may be required for particular applications or cleaning
systems.
8.3.2 Hot-Water Cleaning—Hot water cleaning removes gross organic and particulate contamination from parts by using low
to moderate heat, detergent, and some mechanical agitation. Equipment used during hot-water cleaning may consist of a spray
system or a cleaning vat with or without suitable agitation of the solution. Hot-water cleaning with detergent can be used where
steam is not required to free and fluidize contaminants. Consideration should be given to the size, shape, and number of parts to
ensure adequate contact between part surfaces and the solution. Solution temperature should be as recommended by the cleaning
agent manufacturer. Water-soluble contaminants are best removed by prompt flushing with sufficient quantities of hot or cold clean
water before the cleaning agents have time to precipitate. The parts are then dried by blowing with dry oil-free air or nitrogen,
which may be heated to shorten the drying time.
8.3.3 Steam Cleaning—Steam cleaning removes organic and particulate contaminants from parts by using pressure, heat, and
sometimes detergents. Some organics are removed by decreasing their viscosity, or “thinning” them with steam heat. Detergent
may be added to disperse and emulsify organics, which allows rinsing of the contaminant by condensed steam. The system should
provide control over steam, water, and detergent flows to maximize efficiency of the detergent’s chemical action, the steam heat
effect, and the steam jet’s scrubbing action.
8.3.4 Caustic and Detergent Cleaning—This method relates to the cleaning of vessels, piping systems, or components either
externally or internally and uses water as the primary solvent. Synthetic detergents and surfactants are combined with additives
such as pH buffers, inhibitors, saponifiers, emulsifiers, antifoaming agents, wetting agents, and others for beneficial effects.
8.3.4.1 Caustic cleaning uses highly alkaline solutions to remove organic contamination such as hydrocarbon oils, grease, and
waxes. Some common alkaline salts available for caustic cleaning are listed in Table 2. Prepared solutions can be used in static
tanks or vessels for component immersion. Alternatively, solutions can be pumped or jetted onto or through components.
Depending on the detergent used, solutions may be alkaline, nontoxic, biodegradable, or noncorrosive. Some detergents may be
toxic or corrosive, and detergent properties should be verified by the manufacturer or supplier. See Guide G127 for selection
criteria. The cleaning solution can be applied by spraying, immersing, or hand swabbing. Normally, caustic cleaning solutions are
applied at temperatures up to 180°F (82.2°C). It is important that the cleaning solution reach all areas of the part to be cleaned.
The cleaning solution can be reused until it becomes ineffective as determined by pH or contaminant concentration analysis.
Experience may establish a contaminant level of the cleaning solution above which a surface cannot be acceptably cleaned.
NOTE 3—Caution: Alkalai cleaners attack aluminum.
8.3.4.2 Aqueous systems have few problems with worker safety compared to most other solvents. They are not flammable or
explosive, and toxicity is low for most formulations. Aqueous systems can be designed to remove particulate and film
contamination. They are especially good for removing inorganic or polar materials. Aqueous cleaning functions by several
mechanisms other than solvency, including saponification, displacement, emulsification, and dispersion. Ultrasonics are especially
suited for aqueous solvents.
8.3.4.3 The part must be thoroughly rinsed to prevent the cleaning solution and contaminants from redepositing on the surface.
The surface must not be allowed to dry between the cleaning and rinsing phases. Frequently, some type of water rinsing helps to
remove the cleaning solution and aids in the drying process. Parts with small crevices and blind channels may be difficult to clean
because of the relatively high surface tension and capillary forces of water-based cleaners. Some aqueous cleaner residues can be
difficult to rinse from surfaces; nonionic surfactants are especially difficult to rinse. A method of determining when rinsing is
complete is to monitor the used rinse water until a pH of 60.2 of the starting water pH is achieved. Parts with complex geometries
may be difficult to dry. Clean, dry, oil-free air or nitrogen, heated if necessary, may be used for drying. Alternatively, vacuum may
be used to achieve desired dryness. Table 3 gives general recommendations for alkaline cleaning. This table lists the metallic
material, type of contaminant to be removed, and the alkaline solution used.
8.3.4.4 Drying:
TABLE 2 Common Alkaline Salts (see 8.3.4.1 and 9.4)
A
IUPAC Name Formula Common Name
Sodium hydroxide NaOH Caustic soda
Lye
Sodium metasilicate Na SiO Sodium silicate
2 2
Water glass
Sodium carbonate Na CO Soda ash
2 3
Sodium tetraborate decahydrate Na B O ·10H O Borax
2 4 7 2
Sodium orthophosphate Na PO ·12H O Trisodium phosphate (TSP)
2 4 2
Sodium phosphate tribasic
Sodium pyrophosphate Na P O ·10H O Tetrasodium pyrophosphate
4 2 7 2
Sodium polyphosphate
A
According to the International Union of Pure and Applied Chemistry.
G93/G93M − 19
TABLE 3 Alkaline Chemical Cleaning Materials (see 8.3.4.3)
A B,C
Metal Reason for Cleaning Cleaning Chemicals Other Treatment
Carbon and low alloy steels Removal of heavy soil, grease, and oil Mixtures of sodium hydroxide, Solutions should not be allowed to dry on
carbonates, phosphates and silicates, the part and must be thoroughly rinsed
and synthetic wetting agents
Austenitic stainless steel Removal of heavy soil, grease, light oils, Mixtures of sodium hydroxide,
and cutting fluid carbonates, phosphates and silicates,
and synthetic wetting agents
Copper and alloys Removal of grease, lubricating oil, Mixtures of sodium hydroxide, Usually bright dipped in dichromate acid
drawing compound, oxide, metallic polyphosphates, silicates, carbonates, solution
particles, or other contaminants and wetting agents
Removal of brazing flux Hot water
Aluminum and alloys Removal of grease, oil, and oxide Sodium hydroxide, sodium phosphate, Dilute nitric acid dip to remove smut
and sodium carbonate for etching
Sodium carbonate, sodium silicate,
sodium pyrophosphate, and sodium
metasilicate for nonetching
A
The manufacturer’s specification for application of the cleaning agent shall be strictly enforced.
B
Postchemical Cleaning Treatment—After cleaning using alkaline chemicals, all components shall be thoroughly rinsed, preferably using hot flowing water to aid drying,
unless otherwise specified by the cleaning material supplier. Some components require treatment by using neutralizing solutions after certain cleaning treatments.
C
Thorough rinsing is necessary to avoid stress corrosion risk.
(1) When aqueous cleaning is used on oxygen system components, rinsing and drying are of critical concern. Drying is the
removal of water or other solvents from critical surfaces. The actual process of drying involves a change of state and requires
energy. The amount of energy depends on many factors such as the solvent to be evaporated, the configuration of the hardware,
the temperature of the operation, and the conductivity of the liquid and the hardware. The heat of vaporization for water is an order
of magnitude higher than that for some common chlorofluorocarbon solvents. The removal of vapor is also critical in drying, and
a means for removal of vapor must be provided. This is usually accomplished with a moving dry gas purge.
(2) In selection of a drying process, consideration must be given to the level of dryness required. The user should evaluate each
method for the specific application intended. There are three basic water removal methods commonly used:
(a) Physical—actual removal of liquid such as scraping, wiping, centrifuging, or blowing.
(b) Solvent—wetting the part with a higher vapor pressure liquid to displace the water, such as with alcohol or
hydrofluorocarbons.
(c) Evaporation—adding energy and physically removing the vapor such as drying by oven, air, or purge.
(3) Small- and medium-size hardware drying is often done in filtered gas-purged ovens. System and tank drying may be
achieved by purging with a clean, flowing, dry gas, usually nitrogen or air. Care must be taken in measuring the dew point of a
flowing gas. It is possible to inadvertently measure the dryness of the purge gas only. To sample correctly, a lock-up and
pressurization procedure, with a time allowance interval, is necessary. Items dried with a flowing, heated, dry gas purge are usually
considered dry when the dew point of the exit gas is within 5°F (3°C) of the purge gas.
(4) Dryness is measured in many ways:
(a) Relative humidity,
(b) Dew point,
(c) Unit mass of water per unit mass of gas (ppm),
(d) Unit volume of water per unit volume of gas (v/v), and
(e) Moles of water per moles of air.
(5) Oxygen systems are typically considered dry at equilibrium exit gas dew points of from 0°F (-18°C) to as low as -70°F
(-57°C) depending on the specific application. The choice depends on many variables such as cost, time, use temperature, and
effects of moisture on components. Industrial gases are easily obtained with dew points of -40°F (-40°C), a common specification
level for oxygen system dryness.
8.3.5 Semiaqueous Cleaning:
8.3.5.1 Semiaqueous cleaning uses hydrocarbon-water emulsions to remove heavy contaminants from part surfaces with organic
solvents dispersed in an aqueous medium by an emulsifying agent. The cleaning action of emulsion cleaners combines the
advantages of both the aqueous and organic phases.
(1) Many emulsion cleaners are commercially available and are composed of petroleum-derived solvents and surfactants that
render them emulsifiable. Some emulsion cleaners tend to separate into individual solutions if left standing for extended periods,
and it may be necessary to periodically agitate them so that they remain emulsified. It is important that two-part mixtures are not
allowed to separate, to preclude only part of the mixture being removed from the system. Emulsion cleaners are normally applied
to parts by soaking, spraying, or swabbing. Emulsion cleaners must be removed by rinsing and subsequent cleaning operations.
8.3.5.2 One type of semiaqueous material is a water emulsion with natural citrus and pine-based terpenes. Semiaqueous cleaners
are either emulsified in water and applied in a manner similar to standard aqueous cleaners or they are applied in concentrated form
and then rinsed with water. Semiaqueous formulations are compatible with most metals and plastics. They have good cleaning
ability, especially for heavy grease, tar, wax, and hard to remove soils. The semiaqueous formulations are considered nonflammable
G93/G93M − 19
in bulk but can be flammable as a mist. Proper equipment design is essential to minimize risk from flammable mists. Some
formulations can auto-oxidize into an undesirable condition. Material must be verified with the supplier.
8.3.5.3 The cleaning solution must be thoroughly rinsed from the part to prevent contaminants from redepositing on the surface.
The surface must not be allowed to dry between the cleaning and rinsing phases. Semiaqueous residues are especially difficult to
rinse from surfaces. A more thorough analysis than rinse water pH may be required to determine rinse phase completion. Parts with
complex geometries may be difficult to dry. Clean, dry, oil-free air or nitrogen, heated if necessary, may be used for drying.
Alternatively, vacuum may be combined with purging to achieve desired level of dryness. Care must be used to prevent buckling
from external pressure when vacuum is applied.
8.3.6 Acid Cleaning:
8.3.6.1 Acid cleaning is a process in which a solution of mineral acid, organic acid, or acid salt (often in combination with a
wetting agent and detergent) is used to remove oxides, oils, and other contaminants from parts, with or without the application of
heat. Acid cleaning must be carefully controlled to avoid damage to the part surfaces, such as undesired etching or pickling. The
type of cleaning agent selected will depend on the material or part to be cleaned. The following is a general guide for the use of
acid cleaning.
8.3.6.2 Phosphoric acid cleaning agents can be used for most metals. These agents will remove oxides, light rust, light soils,
and fluxes.
8.3.6.3 Hydrochloric acid cleaning agents are recommended only for carbon and low alloy steels. These agents will remove rust,
scale, and oxide coatings and will strip chromium, zinc, and cadmium platings. Certain acidic solutions, including hydrochloric
or nitric acids, should contain an inhibitor to prevent harmful attacks on base metals. Hydrochloric acid should not be used on
stainless steel since it may cause stress corrosion or stress corrosion cracking.
8.3.6.4 Chromic and nitric acid cleaning compounds are recommended for aluminum and copper and their alloys. These
compounds are not true cleaning agents, but are used for deoxidizing, brightening, and for removing black residue that forms
during cleaning with an alkaline solution. Some compounds are available as liquids, and others as powders. They are mixed in
concentrations of 5 to 50 % in water, depending on the cleaning agent and the amount of oxide or scale to be removed.
8.3.6.5 Acid cleaning requires a storage or an immersion tank, recirculation pump, associated piping, and valving compatible
with the cleaning solution. Common techniques for acid cleaning are immersion, swabbing, and spraying. Acid cleaning
compounds should not be used unless their application and performance are known or are discussed with the cleaning compound
manufacturer. The manufacturer’s recommendations regarding concentration and temperature should be followed for safe handling
of the cleaning agent. After acid cleaning, surfaces must be thoroughly rinsed with water equal to that described in 8.3.1 to remove
all traces of acid and then thoroughly dried after the final water rinse. To minimize staining, do not allow surfaces to dry between
successive steps of the acid cleaning and rinsing procedure. A neutralizing treatment may be required under some conditions.
Neutralization must be followed by repeated water rinsing to remove all traces of the neutralizing agent. If drying is required, it
can be completed with heated or unheated, dry, oil-free air or nitrogen. Table 4 gives typical acid solutions for cleaning various
types of metallic materials.
8.3.7 Solvent Cleaning—This cleaning or degreasing method was once considered to be the principal procedure for removal of
soluble organic contaminants from components to be used in oxygen service and was suitable for use with most metals. The use
and attractiveness of chlorinated solvents as cleaning solutions, however, have been limited by environmental concerns and
legislative restrictions. Chlorinated solvents are being replaced by aqueous or semiaqueous detergents or emulsion solutions, often
in conjunction with deionized water as part of the process. Alcohols, ethers, and other specialized solvents are used in unique
cleaning applications where their hazards are warranted due to process restrictions. A list of common solvents appears in 11.4.2
and Table 5. This method is limited by the ability of the solvent to reach and dissolve any contaminants present. Before starting
any cleaning operation, a reference sample of fresh clean solvent should be set aside to use as a base reference. At intervals
throughout the procedure, samples of used solvent can be compared with the reference sample to determine the level of
TABLE 4 Acid Chemical Cleaning Materials (see 8.3.6.5)
A B
Metal Reason for Cleaning Cleaning Chemicals Other Treatment
Carbon and low alloy steels Removal of scale and oxide films Hydrochloric or sulfuric acid and wetting Dilute alkali dip to neutralize acid
(pickling) agents or treatment with inhibitor
Removal of light rust Citric, sulfuric, and phosphoric acids Light scrubbing action helpful
Removal of grease, oil, or drawing Phosphoric acid and synthetic detergents
compound mixture
Cast iron Removal of oxide Chromic and sulfuric acid
Austenitic stainless steels Removal of oxide, tarnish and scale and Chromic, sulfuric, and hydrofluoric acid, or Nitric acid solution used to
metallic deposits/contaminants nitric, hydrofluoric, and phosphoric acids brighten
Copper and alloys Removal of scale and oxide (pickling) Hydrochloric or sulfuric acid
Brightening Sulfuric, nitric, and hydrochloric acids
Aluminum and alloys Removal of oxide (etch cleaning) Nitric acid solution used to brighten Hydroxide solutions
A
The manufacturer’s specification for application of the cleaning agent should be strictly observed or the properties of the metals can be impaired. Time, temperature, and
concentrations are very important.
B
Postchemical Cleaning Treatment—After acid cleaning, all components should be thoroughly rinsed, preferably using flowing hot water to aid drying, unless otherwise
specified by the cleaning material supplier. Some components require treatment with neutralizing solutions after certain cleaning treatments.
G93/G93M − 19
TABLE 5 Common Solvents (see 8.3.7)
Chemical Class Common Examples
Hydrochlorofluorocarbons Asahiklin AK 225
Hydrofluorocarbon DuPont Vertrel XF
DuPont Vertrel MCA
Hydrofluoroether 3M HFE 7100
3M HFE 71DE
contamination. Methods of determining contamination can be by comparison to the color of the reference sample, by fluorescence
under ultraviolet light, by analysis, or by evaporation. Clean glass bottles must be used to hold samples.
8.3.7.1 After completion of any solvent cleaning method, all gross residual cleaning fluid must be drained from the component
to prevent drying in pools. The component shall then be purged and dried with heated dry, oil-free air or nitrogen. Small
components may be air dried if appropriate, so long as they do not become recontaminated.
8.3.7.2 Solvent cleaning may be performed using any of the methods previously discussed such as swabbing and spraying.
Components and disassembled parts can also be cleaned by immersion in a solvent tank and applying agitation. The process can
be improved by the use of ultrasonic cleaning techniques. Cleaning by forced circulation of a liquid solvent flow through the
component can also be carried out. The duration of cleaning by circulation shall be continued using clean solvent until the used
solvent emerges from the component as clean as the reference sample.
8.3.7.3 Solvents frequently require inhibitors to control corrosion reactions. The addition of inhibitors may require monitoring
to ensure continued effectiveness. This method is often applied to assemblies that cannot be disassembled, to large size
components, to prefabricated circuits, and pipeworks.
8.3.8 Solvent Cleaning Hazards:
8.3.8.1 Take care that generous ventilation is provided in solvent cleaning areas to prevent workers from breathing excessive
amounts of solvent vapor or decomposition products. Vapor from any halogenated solvents is a powerful anesthetic. Inhaled in
small quantities, it will cause d
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